1. Field of the Invention
The present invention relates to signal detection techniques. In particular, the present invention relates to reducing memory usage in systems and methods that use non-coherent accumulation in detecting signals.
2. Discussion of the Related Art
A receiver of a navigation system detects positioning signals from the Global Positioning System (GPS) to estimate its location. One common detection method uses non-coherent accumulation, which is a technique for searching for the code phase and frequency of a received signal involving accumulating either the modulus, or the squared modulus, of complex correlations of a reference signal and the received signal. Depending upon the relative amount of signal and noise present in the received signal, the correlation values will have different distributions. Typically, an accumulated sum is stored in memory for each trial combination of code-phase and frequency. Signal detection occurs when the statistical properties of an accumulated sum indicate that a signal is almost certainly present. Memory is a significant cost in such a navigation system, as a large number of such accumulated sums are kept in memory to achieve high resolution in detection.
A number of U.S. patent applications disclose applicable signal processing techniques relevant to a navigation system of the present application:                1. Signal Acquisition using Data Bit Information, Ser. No. 09/888,228 filed Jun. 22, 2001, now U.S. Pat. No. 6,512,379;        2. Synthesizing Coherent Correlation Sums at One or Multiple Carrier Frequencies Using Correlation Sums Calculated at a Coarse Set of Frequencies, Ser. No. 09/888,227, filed Jun. 22, 2001, now U.S. Pat. No. 7,164,736;        3. Extracting Fine-Tuned Estimates from Correlation Functions Evaluated at Limited Number of Values, Ser. No. 09/888,338, filed Jun. 22, 2001, now U.S. Pat. No. 7,027,534;        4. Determining the Spatio-Temporal and Kinematic Parameters of a Signal Receiver and its Clock by Information Fusion, Ser. No. 09/888,229, filed Jun. 22, 2001, now U.S. Pat. No. 6,542,116;        5. Determining Location Information Using Sampled Data Containing Location Determining Signals And Noise Ser. No. 09/888,337, filed Jun. 22, 2001, now U.S. Pat. No. 6,535,163;        6. Method for optimal search scheduling in satellite acquisition, Ser. No. 10/126,853, filed on Apr. 19, 2002, now U.S. Pat. No. 6,836,241;        7. System and method to estimate the location of a receiver in a multi path environment, Ser. No. 10/237,556, filed on Sep. 6, 2002, now U.S. Pat. No. 7,030,814;        8. System and method to estimate the location of a receiver, Ser. No. 10/237,557, filed on Sep. 6, 2002, now U.S. Pat. No. 7,069,019; and        9. Multifunction device with positioning system and shared processor, Ser. No. 10/286,360, filed on Nov. 1, 2002, now U.S. Pat. No. 7,132,980.        
The above copending patent applications, which are each assigned to SirF Technology, Inc., are hereby incorporated by reference in their entirety.